Add guest mode functionality for read-only access

- Implement guest mode for unauthenticated users
- Allow file viewing and downloading without login
- Hide create/edit/delete functions for guests
- Add guest mode banner with login prompt
- Add read-only badges for guest accessible files
- Include permission checks for all CRUD operations
- Add responsive guest mode styling
- Support both online (Supabase) and offline (localStorage) modes

Features:
• Guest users can view all files and download attachments
• Authentication required for create, edit, delete operations
• Seamless transition between guest and authenticated modes
• User-friendly guest experience with clear login prompts

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

supabase-config.js

@@ -100,14 +100,19 @@ const SupabaseHelper = {
     async getFiles(userId) {
         if (!supabase) throw new Error('Supabase가 초기화되지 않았습니다.');
         
-        const { data, error } = await supabase
+        let query = supabase
             .from('files')
             .select(`
                 *,
                 file_attachments (*)
-            `)
-            .eq('user_id', userId)
-            .order('created_at', { ascending: false });
+            `);
+            
+        // 공개 파일 요청이 아닌 경우에만 사용자 ID로 필터링
+        if (userId !== 'public') {
+            query = query.eq('user_id', userId);
+        }
+        
+        const { data, error } = await query.order('created_at', { ascending: false });
             
         if (error) throw error;
         return data;